Topic 16 HL - Chemical Kinetics Flashcards
rate of reaction =
change in concentration / time
reactions may occur by more than one step but …
the slowest step determines the rate of reaction (rate determining step RDS)
the molecularity of an elementary step is …
the number of reactant particles taking part in that step
the order of reaction can be either …
integer or fractional nature
the order of reaction can describe …
with respect to a reactant, the number of particles taking part in the rate determining step
rate equations can only be determined…
experimentally because the orders can only be deduced empirically
the value of the rate constant (k) is affected by …
temperature and its units are determined from the overall order of the reaction
catalysts …
alter a reaction mechanism, introducing a step with lower activation energy
overall reaction order =
m + n
the orders with respect to each reactant, which convey how sensitive the rate of reaction is to change in the concentrations or A and B
a catalyst is a substance that …
increases the rate of a chemical reaction but is not consumed in the reaction itself. it provides an alternative pathway for the reaction and lowers the activation energy
the contact process
1) S(s) + O2(g) –> SO2(g)
2) SO2(g) + O2(g) 2SO3(g)
the catalyst used is vanadium (V) oxide V2O5(s) which is a heterogenous catalyst
3) SO3(g) + H2SO4(l) –> H2S2O7(l). reacts with concentrated sulphuric acid to produce oleum
4) H2S2O7(l) + H2O(l) –> 2H2SO4(aq) sulphuric acid
why is the oleum formed first?
the direct reaction between sulphur trioxide and water is too vigorous
individual steps in a reaction mechanism are called …
elementary steps / elementary reaction / elementary process
elementary steps are classified by their …
molecularity, which represents the number of molecules or atoms involved as reactants in the elementary step
unimolecular
single molecule involved in an elementary step
bimolecular
two molecules or atoms involved in collision in an elementary step
termolecular
three molecules or atoms involved in collision in an elementary step
each elementary step has its own…
rate constant, k, and its own activation energy Ea
reaction: NO2(g) + CO2(g) –> NO(g) + CO2(g)
step 1) NO2(g) + NO2(g) –> NO(g) + NO3(g) step 1 is bimolecular. cross out intermediates (NO2 and NO3)
step 2) NO3(g) + CO(g) –> NO2(g) + CO2(g) step 2 is bimolecular. cross out intermediates (NO3 and NO2
why is NO3 an intermediate?
it is formed in step 1 and then consumed subsequently in step 2
how do you determine the slow step?
the rate of the overall reaction is equal to the rate of the slow step
what is the experimental rate of reaction for the NO2 and CO2 reaction?
for any temperature under 498K, the experimental equation for the reaction is:
rate = k(NO2)^2
the Arrhenius equations uses …
temperature dependence of the rate constant to determine the activation energy
what must be fulfilled for a chemical reaction to occur between two reactant particles?
1) the two particles must collide with each other, that is there must be physical contact
2) the colliding particles must have correct mutual orientation
3) the colliding particles must have sufficient kinetic energy to initiate the reaction itself
